Khan, Nazir; Bashir, Zahir; Price, Duncan M.; Liquid crystalline aromatic polyesters formed with terephthalic acid, phenyl hydroquinone, and naphthalene or anthracene. Journal of Applied Polymer Science 58(9) (1995) 1509-1516
The synthesis and characterisation of aromatic copolyesters containing terephthalic acid and phenylhydroquinone as the major constituents and either 1,4-naphthalenediol or 1,4-anthracenediol as the minority comonomer is described. Both polymers melted in the vicinity of 300°C, giving birefringent fluids. Optical microscopy showed Schlieren textures consisting predominantly of inversion walls characteristic of the nematic phase. The clearing temperature was in the vicinity of 460°C, but was accompanied by charring. DSC experiments showed a high glass transition temperature of 130-160°C for both polymers. Crystal-nematic and nematic-isotropic endotherms were observed on heating; however, degradation took place near the isotropisation temp. Thus, on cooling, the sequence was reversible only if the previous heating was beyond the crystal-nematic but below the isotropisation temp. The polymers were stable in terms of gross wt. loss until about 450°C, though there were indications that crosslinking occurred above about 400°C over a short period of time. The polymers formed low-viscosity injection-moulding compounds, but to use them effectively, it would require mould-gate designs that reduce the "jetting" tendency for liquid crystal polymer melts, which result in weld lines.
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